1. Field of the Invention
The invention relates to a drive system and a vehicle including a drive system.
2. Description of Related Art
In recent years, electromotive vehicle, such as electric vehicles, hybrid vehicles and fuel-cell vehicles, that travel by driving a motor with electric power stored in a power supply device have become a focus of attention. These electromotive vehicles include a converter that outputs high-voltage direct-current power by stepping up voltage, supplied from the power supply device, to a predetermined voltage and a capacitor that smoothes the voltage output from the converter. These electromotive vehicles include an inverter that converts direct-current power, output from the converter, to alternating-current power and a drive motor that is driven by alternating-current power output from the inverter.
In such an electromotive vehicle, in order to improve the safety of the vehicle, it is required to quickly discharge the energy of high-voltage direct-current power stored in the capacitor in the event of collision of the vehicle. For example, in order to satisfy the standard associated with protection of an electric power control device, which is regulated in United States laws and regulations, that is, Federal Motor Vehicle Safety Standard (FMVSS) 305, it is required to set the voltage of the capacitor to a predetermined value or below within 5 seconds from a collision.
As a technique for rapidly discharging electric charge stored in a smoothing capacitor, there is, for example, a technique for causing the smoothing capacitor to generate heat by connecting a plurality of resistors to the smoothing capacitor.
In addition, there is a technique for adjusting the amount of electric charge that is stored in a smoothing capacitor by connecting a capacitor in parallel with the smoothing capacitor (for example, see Japanese Patent Application Publication No. 2011-210026 (JP 2011-210026 A) and Japanese Patent Application Publication No. 2009-232537 (JP 2009-232537 A)).
However, in the above-described related techniques, a resistor having a large rated power is required, so a system including a heat dissipation cooling device may increase in size. In addition, it is difficult to control the voltage of the smoothing capacitor only by connecting a capacitor in parallel with the smoothing capacitor.